Chronic obstructive pulmonary disease other diagnostic studies

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Philip Marcus, M.D., M.P.H. [2]; Associate Editor(s)-In-Chief: Cafer Zorkun, M.D., Ph.D. [3]

Overview

The diagnosis of COPD is confirmed by spirometry, a test that measures the forced expiratory volume in one second (FEV₁), which is the greatest volume of air that can be breathed out in the first second of a large breath. Spirometry also measures the forced vital capacity (FVC), which is the greatest volume of air that can be breathed out in a whole large breath. Normally, at least 70% of the FVC comes out in the first second (i.e. the FEV₁/FVC ratio is >70%). A ratio less than normal defines the patient as having COPD.

File:COPD.JPG

A chest X-ray demonstrating severe COPD. Note the small size of the heart in comparison to the lungs.

Spirometry

COPD is particularly characterized if a ratio of forced expiratory volume over 1 second (FEV₁) to forced vital capacity (FVC) being < 0.7 and the FEV₁ < 70% of the predicted value when compared with a matched control. , (see Spirometry). Normally, at least 70% of the FVC comes out in the first second (i.e. the FEV₁/FVC ratio is >70%). A ratio less than normal defines the patient as having COPD. More specifically, the diagnosis of COPD is made when the FEV₁/FVC ratio is <70%. The GOLD criteria also require that values are after bronchodilator medication has been given to make the diagnosis, and the NICE criteria also require FEV1%. According to the ERS criteria, it is FEV1% predicted that defines when a patient has COPD, that is, when FEV1% predicted is < 88% for men, or < 89% for women.

Spirometry can help to determine the severity of COPD. The FEV₁ (measured after bronchodilator medication) is expressed as a percentage of a predicted "normal" value based on a person's age, gender, height and weight:

The severity of COPD also depends on the severity of dyspnea and exercise limitation. These and other factors can be combined with spirometry results to obtain a COPD severity score that takes multiple dimensions of the disease into account.

The severity of COPD can be classified as follows using spirometry (see above):

Severity	FEV1 /FVC	FEV1 % predicted
At risk	>0.7	≥80
Mild COPD	≤0.7	≥80
Moderate COPD	≤0.7	50-80
Severe COPD	≤0.7	30-50
Very Severe COPD	≤0.7	<30 or 30-50 with Chronic Respiratory Failure symptoms

Other tests

On chest x-ray, the classic signs of COPD are overexpanded lung (hyperinflation), a flattened diaphragm, increased retrosternal airspace, and bullae. It can be useful to help exclude other lung diseases, such as pneumonia, pulmonary edema or a pneumothorax. Complete pulmonary function tests with measurements of lung volumes and gas transfer may also show hyperinflation and can discriminate between COPD with emphysema and COPD without emphysema. A high-resolution computed tomography scan of the chest may show the distribution of emphysema throughout the lungs and can also be useful to exclude other lung diseases.

A blood sample taken from an artery, i.e. Arterial Blood Gas (ABG), can be tested for blood gas levels which may show low oxygen (hypoxaemia) and/or high carbon dioxide (respiratory acidosis if pH is also decreased). A blood sample taken from a vein may show a high blood count (reactive polycythemia), a reaction to long-term hypoxemia.

References

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